Flux Control Analysis of the Rate of Photosynthetic CO2 Assimilation
Metabolic flux control analysis offers an opportunity to understand how fluxes are determined and thus how they can be increased. Enzymes are assigned a control coefficient (usually between zero and one) which is a measure of the degree to which the flux is sensitive to small changes in enzyme concentration. This chapter examines research on the application of control analysis to the photosynthetic system of C3 plants, specifically the net rate of CO2 fixation. Control coefficients have been measured for a number of the enzymes, typically by reducing the concentration of a target enzyme in transgenic plants then comparing their flux and enzyme concentrations to those of the wild type. There have been surprisingly many difficulties with this approach. Firstly, many transgenic plants have markedly lower enzyme concentrations than the wild type, so it has been difficult to make accurate estimations of the enzyme-flux relationship in the vicinity of the wild type value. Second, natural variation, compounded by variation due to a lack of precision in measurements, has often required a very large number of replicates in order to detect significant values. Many studies have not used sufficient replication. Third, confounding variables, such as ontogenetic variation and untargeted changes in the concentration of other enzymes, have not always been identified and taken into account. As a consequence of these challenges, there are few studies in which control coefficients have been detected with a high degree of certainty. This situation is set to improve, however, with the use of transgenic plants with both an increased and decreased target enzyme concentration. Several such studies have now been published, and in two cases, estimates of the control coefficients have been markedly improved.
KeywordsTitration Respiration Assimilation Fructose NADP
Unable to display preview. Download preview PDF.
- Cowan IR (1986) Economics of carbon fixation in higher plants. In: Givnish, TJ (ed) On the Economy of Plant Form and Function, pp 133–170. Cambridge University Press, CambridgeGoogle Scholar
- Haake V, Geiger M, Walch-Liu P, Engels C, Zrenner R and Stitt M (1999) Changes in aldolase activity in wild-type potato plants are important for acclimation to growth irra-diance and carbon dioxide concentration, because plastid aldolase exerts control over the ambient rate of photosynthesis across a range of growth conditions. Plant J 17: 479–489CrossRefGoogle Scholar
- Hajirezaei MR, Peisker M, Tschiersch H, Palatnik JF, Valle EM, Carrillo N and Sonnewald U (2002) Small changes in the activity of NADP+-dependent ferredoxin oxi-doreductase lead to impaired plant growth and restrict photosynthetic activity in transgenic tobacco plants. Plant J 29: 281–293PubMedCrossRefGoogle Scholar
- Häusler RE, Schlieben NH and Flügge UI (2000) Control of carbon partitioning and photosynthesis by the triose phosphate/phosphate translocator in transgenic tobacco plants (Nicotiana tabacum). II. Assessment of control coefficients of the triose phosphate/phosphate transloca-tor. Planta 210: 383–390PubMedCrossRefGoogle Scholar
- Price GD, Von Caemmerer S, Evans JR, Yu JW, Lloyd J, Oja V, Kell P, Harrison K, Gallagher A and Badger MR (1994) Specific reduction of chloroplast carbonic anhy-drase activity by antisense RNA in transgenic tobacco plants has a minor effect on photosynthetic CO2 assimilation. Planta 193: 331–340CrossRefGoogle Scholar
- Price GD, Evans JR, Von Caemmerer S, Yu JW and Badger MR (1995a) Specific reduction of chloroplast glycer-aldehyde 3-phosphate dehydrogenase activity by antisense RNA reduces CO2 assimilation via a reduction in ribulose bisphosphate regeneration in transgenic tobacco plants. Planta 195: 369–378CrossRefGoogle Scholar
- Price GD, Yu JW, Von Caemmerer S, Evans JR, Chow WS, Anderson JM, Hurry V and Badger MR (1995b) Chloroplast cytochrome b(6)/f and ATP synthase complexes in tobacco — transformation with antisense RNA against nuclear encoded transcripts for the Rieske FeS and ATP-delta polypeptides. Aust J Plant Physiol 22: 285–297Google Scholar
- Price GD, Von Caemmerer S, Evans JR, Siebke K, Anderson JM and Badger MR (1998) Photosynthesis is strongly reduced by antisense suppression of chloroplastic cytochrome bf complex in transgenic tobacco. Aust J Plant Physiol 25: 445–452Google Scholar
- Quick WP, Fichtner K, Schulze E-D, Wendler R, Leegood RC, Mooney H, Rodermel SR, Bogorad L and Stitt M (1992) Decreased ribulose-l,5-bisphosphate carboxy-lase/oxygenase in transgenic tobacco transformed with “antisense” rbcS. IV. Impact on photosynthesis and plant growth altered nitrogen supply. Planta 188: 522–531CrossRefGoogle Scholar
- Woodrow IE and Berry JA (1988) Enzymatic regulation of photosynthetic CO2 fixation in C3 plants. Annu Rev Plant Physiol Plant Mol Biol 39: 533–594Google Scholar